CRP and major depressive disorder: Increased CRP levels have clinical relevance for depression (Miller & Raison, 2016), as CRP ⩾3 mg/L was associated with an increased risk of developing depression later in life (Au, Smith, Gariepy, & Schmitz, 2015), and a lack of response to antidepressant medication (Chamberlain et al., 2019; Zhang et al., 2019).